3DIC interconnect devices and methods of forming same

ABSTRACT

An interconnect device and a method of forming the interconnect device are provided. Two integrated circuits are bonded together. A first opening is formed through one of the substrates. One or more dielectric films are formed along sidewalls of the first opening. A second opening is formed extending from the first opening to pads in the integrated circuits, while using some of the pads as hard masks. The first opening and the second opening are filled with a conductive material to form a conductive plug.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation-in-part of U.S. patent application Ser. No. 14/467,981, entitled “3DIC Interconnect Devices and Methods of Forming Same,” filed on, Aug. 25, 2014, which claims the benefit of U.S. Provisional Application Ser. No. 62/004,794, filed on May 29, 2014, entitled “Through Oxide Vias and Methods of Forming Same,” all of which are incorporated herein by reference.

BACKGROUND

The semiconductor industry has experienced rapid growth due to continuous improvements in the integration density of a variety of electronic components (e.g., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size (e.g., shrinking the semiconductor process node towards the sub-20 nm node), which allows more components to be integrated into a given area. As the demand for miniaturization, higher speed and greater bandwidth, as well as lower power consumption and latency has grown recently, there has grown a need for smaller and more creative packaging techniques of semiconductor dies.

As semiconductor technologies further advance, stacked semiconductor devices, e.g., 3D integrated circuits (3DIC), have emerged as an effective alternative to further reduce the physical size of a semiconductor device. In a stacked semiconductor device, active circuits such as logic, memory, processor circuits and the like are fabricated on different semiconductor wafers. Two or more semiconductor wafers may be stacked on top of one another to further reduce the form factor of the semiconductor device.

Two semiconductor wafers may be bonded together through suitable bonding techniques. The commonly used bonding techniques include direct bonding, chemically activated bonding, plasma activated bonding, anodic bonding, eutectic bonding, glass frit bonding, adhesive bonding, thermo-compressive bonding, reactive bonding and/or the like. An electrical connection may be provided between the stacked semiconductor wafers. The stacked semiconductor devices may provide a higher density with smaller form factors and allow for increased performance and lower power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A-1D are cross-sectional views of various processing steps during fabrication of an interconnect structure between two bonded workpieces in accordance with some embodiment.

FIG. 1E illustrates various top views of conductive lines in accordance with some embodiments.

FIGS. 2-3I are cross-sectional views of an interconnect structure between two bonded workpieces in accordance with some embodiment.

FIG. 4 is a flow diagram illustrating a method of forming an interconnect structure between two bonded workpieces in accordance with some embodiment.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

The present disclosure will be described with respect to embodiments in a specific context, namely, a method for forming interconnect structures for a stacked semiconductor device. Other embodiments, however, may be applied to a variety of semiconductor devices. Hereinafter, various embodiments will be explained in detail with reference to the accompanying drawings.

FIGS. 1A-1D illustrate various intermediate steps of forming an interconnect structure between two bonded workpieces in accordance with a first embodiment. Referring first to FIG. 1A, a first workpiece 100 and a second workpiece 200 is shown prior to a bonding process in accordance with various embodiments. In an embodiment, the second workpiece 200 has similar features as the first workpiece 100, and for the purpose of the following discussion, the features of the second workpiece 200 having reference numerals of the form “2xx” are similar to features of the first workpiece 100 having reference numerals of the form “1xx.” The various elements of the first workpiece 100 and the second workpiece 200 will be referred to as the “first <element>1xx” and the “second <element>2xx,” respectively.

In an embodiment, the first workpiece 100 comprises a first substrate 102. The first substrate 102 may be formed of silicon, although it may also be formed of other group III, group IV, and/or group V elements, such as silicon, germanium, gallium, arsenic, and combinations thereof. The first substrate 102 may also be in the form of silicon-on-insulator (SOI). The SOI substrate may comprise a layer of a semiconductor material (e.g., silicon, germanium and/or the like) formed over an insulator layer (e.g., buried oxide and/or the like), which is formed on a silicon substrate. In addition, other substrates that may be used include multi-layered substrates, gradient substrates, hybrid orientation substrates, any combinations thereof and/or the like.

The first substrate 102 may further comprise a variety of electrical circuits (not shown). The electrical circuits formed on the first substrate 102 may be any type of circuitry suitable for a particular application. In accordance with some embodiments, the electrical circuits may include various n-type metal-oxide semiconductor (NMOS) and/or p-type metal-oxide semiconductor (PMOS) devices such as transistors, capacitors, resistors, diodes, photo-diodes, fuses and/or the like.

The electrical circuits may be interconnected to perform one or more functions. The functions may include memory structures, processing structures, sensors, amplifiers, power distribution, input/output circuitry and/or the like. One of ordinary skill in the art will appreciate that the above examples are provided for illustrative purposes only and are not intended to limit the various embodiments to any particular applications.

In some embodiments, the electrical circuits are electrically isolated using one or more first shallow trench isolation (STI) regions 109 as illustrated in FIG. 1A. In the illustrated embodiment, the first substrate 102 is patterned using, for example, photolithographic masking and etching process to form openings in the first substrate 102. Subsequently, the openings are filled with a dielectric material, and portions of the dielectric material overfilling the openings are removed using, for example, an etch process, chemical mechanical polishing (CMP), or the like. The one or more first STI regions 109 may be formed of suitable dielectric materials such as silicon oxide, silicon nitride, silicon oxynitride, fluoride-doped silicate glass (FSG), low-k dielectrics such as carbon doped oxides, extremely low-k dielectrics such as porous carbon doped silicon dioxide, a polymer such as polyimide, combinations of these, or the like. In some embodiments, the one or more first STI regions 109 are formed through a process such as chemical vapor deposition (CVD), plasma-enhanced CVD (PECVD), or a spin-on process, although any acceptable process may be utilized.

Referring further to FIG. 1A, first inter-metal dielectric (IMD) layers 104 are formed over the first substrate 102. As shown in FIG. 1A, the first IMD layers 104 may comprise first conductive lines 108 a-108 i (collectively referred to as first conductive lines 108). The first IMD layers 104 and the first conductive lines 108 form first metallization layers over the first substrate 102. Generally, metallization layers are used to interconnect the electrical circuitry to each other and to provide an external electrical connection. As shown in FIG. 1A, the first workpiece 100 comprises nine conductive lines (such as the first conductive lines 108 a-108 i). In other embodiments, number of conductive lines may be less or more than nine, and may vary according to the design requirement of the first workpiece 100.

The first IMD layers 104 may be formed, for example, of a low-K dielectric material, such as phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), fluorinated silicate glass (FSG), undoped silicate glass (USG), SiO_(x)C_(y), SiOCH, Spin-On-Glass, Spin-On-Polymers, high-density plasma (HDP) oxide, tetraethyl orthosilicate (TEOS), plasma-enhanced TEOS (PETEOS), fluorine-doped silicon oxide, carbon-doped silicon oxide, porous silicon oxide, porous carbon-doped silicon oxide, black diamond, organic polymers, silicone based polymers, compounds thereof, composites thereof, combinations thereof, or the like, by any suitable method known in the art, such as spin-on, atomic layer deposition (ALD), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), the like, or a combination thereof.

The first conductive lines 108 may be formed through any suitable formation process (e.g., lithography with etching, damascene, dual damascene, or the like) and may be formed using suitable conductive materials such as copper, aluminum, aluminum alloys, copper alloys or the like. In some embodiments, each of the first conductive lines 108 may further comprise a diffusion barrier layer and/or an adhesion layer (not shown) to protect the first IMD layers from metal poisoning. The diffusion barrier layer may comprise one or more layers of TaN, Ta, TiN, Ti, CoW, or the like, and may be deposited by physical vapor deposition (PVD), or the like.

FIG. 1A further illustrates a first bonding layer 106 formed over the first IMD layers 104 of the first workpiece 100. As described below the first bonding layer 106 is subsequently used to bond the first workpiece 100 and the second workpiece 200, and may comprise any suitable material for bonding. In some embodiments, the first bonding layer 106 is a first passivation layer 106. The first passivation layer 106 may be formed of one or multiple layers comprising silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, silicon oxycarbide, undoped silicon glass, phosphosilicate glass, compounds thereof, composites thereof, combinations thereof, or the like, deposited by any suitable method, such as spin-on, CVD, PECVD, or the like. These materials and processes are provided as examples and other materials and processes may be used.

It should also be noted that one or more etch stop layers (not shown) may be positioned between adjacent layers of the first workpiece 100, e.g., the first IMD layers 104 and the first substrate 102, or between individual layers of the first IMD layers 104. Generally, the etch stop layers provide a mechanism to stop an etching process when forming vias and/or contacts. The etch stop layers are formed of a dielectric material having a different etch selectivity from adjacent layers, e.g., the underlying first substrate 102 and the overlying first IMD layers 104. In an embodiment, etch stop layers may be formed of SiN, SiCN, SiCO, CN, combinations thereof, or the like, deposited by CVD or PECVD techniques.

In an embodiment, the first workpiece 100 is a backside illumination sensor (BIS) and the second workpiece 200 is an application-specific integrated circuit (ASIC) device. In this embodiment, the electrical circuitry includes photo active regions, such as photo-diodes formed by implanting impurity ions into the epitaxial layer. Furthermore, the photo active regions may be a PN junction photo-diode, a PNP photo-transistor, an NPN photo-transistor or the like. The BIS sensor may be formed in an epitaxial layer over a silicon substrate. The ASIC device may comprise a plurality of logic circuits such as an analog-to-digital converter, a data processing circuit, a memory circuit, a bias circuit, a reference circuit, any combinations thereof and/or the like.

In an embodiment, the first workpiece 100 and the second workpiece 200 are arranged with device sides (also referred as front sides) of the first substrate 102 and the second substrate 202 facing each other as illustrated in FIG. 1A. As discussed in greater detail below, an opening will be formed extending from a backside (opposite the device side) of the first workpiece 100 to the selected portions of the second conductive lines 208 of the second workpiece 200, such that portions of selected first conductive lines 108 of the first workpiece 100 will also be exposed. The opening will be subsequently filled with a conductive material, thereby forming an electrical contact on the backside of the first workpiece 100 to the conductive lines of the first workpiece 100 and the second workpiece 200.

FIG. 1B illustrates the first workpiece 100 and the second workpiece 200 after bonding in accordance with an embodiment. As shown in FIG. 1A, the first workpiece 100 will be stacked and bonded on top of the second workpiece 200. In the illustrated embodiment, the first workpiece 100 and the second workpiece 200 are bonded using dielectric-to-dielectric bonding (e.g., oxide-to-oxide bonding) by bonding the first passivation layer 106 to the second passivation layer 206. In other embodiments, the first workpiece 100 and the second workpiece 200 may be bonded using, for example, a direct bonding process such as metal-to-metal bonding (e.g., copper-to-copper bonding), metal-to-dielectric bonding (e.g., oxide-to-copper bonding), hybrid bonding (e.g., dielectric-to-dielectric and metal-to-metal bonding), any combinations thereof and/or the like.

It should be noted that the bonding may be at wafer level, wherein the first workpiece 100 and the second workpiece 200 are bonded together, and are then singulated into separated dies. Alternatively, the bonding may be performed at the die-to-die level, or the die-to-wafer level.

After the first workpiece 100 and the second workpiece 200 are bonded, a thinning process may be applied to the backside of the first workpiece 100. In an embodiment in which the first substrate 102 is a BIS sensor, the thinning process serves to allow more light to pass through from the backside of the first substrate to the photo-active regions without being absorbed by the substrate. In an embodiment in which the BIS sensor is fabricated in an epitaxial layer, the backside of the first workpiece 100 may be thinned until the epitaxial layer is exposed. The thinning process may be implemented by using suitable techniques such as grinding, polishing, a SMARTCUT® procedure, an ELTRAN® procedure, and/or chemical etching.

Referring further to FIG. 1B, a first opening 110 is formed on the backside of the first workpiece 100. As discussed in greater detail below, an electrical connection will be formed extending from a backside of the first workpiece 100 to select ones of the second conductive lines 208 of the second workpiece 200. The first opening 110 represents an opening in which the backside contact will be formed. The first opening 110 may be formed using photolithography techniques. Generally, photolithography techniques involve depositing a photoresist material, which is subsequently irradiated (exposed) and developed to remove a portion of the photoresist material. The remaining photoresist material protects the underlying material from subsequent processing steps, such as etching. A suitable etching process, such as a reactive ion etch (RIE) or other dry etch, an anisotropic wet etch, or any other suitable anisotropic etch or patterning process may be applied to the first substrate 102 of the first workpiece 100. In the illustrated embodiment, the first STI region 109 is used as an etch stop layer, and the first opening 110 is formed in the first substrate 102 as illustrated in FIG. 1B. In some embodiments, the first STI region 109 may be partially etched as illustrated in FIG. 1B.

Also shown in FIG. 1B is an optional anti-reflection coating (ARC) layer 112. The ARC layer 112 reduces the reflection of the exposure light used during the photolithography process to pattern a patterned mask (not shown), which reflection may cause inaccuracies in the patterning. The ARC layer 112 may be formed of a nitride material (e.g., silicon nitride), an organic material (e.g., silicon carbide), an oxide material, high-k dielectric, and the like. The ARC layer 112 may be formed using suitable techniques such as CVD and/or the like.

Other layers may be used in the patterning process. For example, one or more optional hard mask layers may be used to pattern the first substrate 102. Generally, one or more hard mask layers may be useful in embodiments in which the etching process requires masking in addition to the masking provided by the photoresist material. During the subsequent etching process to pattern the first substrate 102, the patterned photoresist mask will also be etched, although the etch rate of the photoresist material may not be as high as the etch rate of the first substrate 102. If the etch process is such that the patterned photoresist mask would be consumed before the etching process is completed, then an additional hard mask may be utilized. The material of the hard mask layer or layers is selected such that the hard mask layer(s) exhibit a lower etch rate than the underlying materials, such as the materials of the first substrate 102.

Referring further to FIG. 1B, a dielectric film 114 is formed over the backside of the first substrate 102 and along sidewalls and a bottom of the first opening 110 in accordance with an embodiment. The dielectric film 114 provides greater passivation and isolation between through via structures and device circuits in addition to the one or more first STI regions 109. In some embodiments, the dielectric film 114 comprises a multilayer structure, which provides greater protection than a single film during, for example, a subsequent etch process to form electrical contacts to selected ones of the first conductive lines 108 and the second conductive lines 208. Additionally, the dielectric film 114 may provide protection against metal ions diffusing into the first substrate 102 and the dielectric layers.

The dielectric film 114 may be formed of various dielectric materials commonly used in integrated circuit fabrication. For example, the dielectric film 114 may be formed of silicon dioxide, silicon nitride or a doped glass layer such as boron silicate glass and the like. Alternatively, dielectric layer may be a layer of silicon nitride, silicon oxynitride, polyamide, a low-k dielectric, or a high-k dielectric, or the like. In addition, a combination of the foregoing dielectric materials may also be used to form the dielectric film 114. In some embodiments, the dielectric film 114 may be formed using suitable techniques such as sputtering, oxidation, CVD and/or the like.

FIG. 1B further illustrates a patterned mask 116 formed over the backside of the first substrate 102 in accordance with an embodiment. The patterned mask 116 may be, for example, a photoresist material that has been deposited, masked, exposed, and developed as part of a photolithography process. The patterned mask 116 is patterned to define a via opening extending through the one or more first STI regions 109 of the first substrate 102, the first IMD layers 104 of the first substrate 102 and at least some of the second IMD layers 204 of the second substrate 202, thereby exposing portions of select ones of the first conductive lines 108 and the second conductive lines 208, as explained in greater detail below.

FIG. 1C illustrates the semiconductor device shown in FIG. 1B after one or more additional etching processes are performed in accordance with an embodiment. A suitable etching process, such as a dry etch, an anisotropic wet etch, or any other suitable anisotropic etch or patterning process, may be performed on the semiconductor device to form a second opening 118.

As illustrated in FIG. 1C, the second opening 118 extends the first opening 110 to the first conductive lines 108 a and 108 b, the first conductive lines 108 c and 108 d, the first conductive lines 108 e and 108 f, and to the second conductive line 208 a. In an embodiment, the first conductive lines 108 are formed of suitable metal materials such as copper, which exhibits a different etching rate (selectivity) than the first IMD layers 104. As such, the first conductive lines 108 a and 108 b as well as the first conductive lines 108 c and 108 d, and the first conductive lines 108 e and 108 f function as hard mask layers for an etching process of the first IMD layers 104. A selective etching process may be employed to etch the first IMD layers 104 rapidly while etching only portions of the first conductive lines 108 a through 108 f in some embodiments. In some embodiments, some or all of the first conductive lines 108 may be dummy conductive lines and may not provide electrical connection between the electrical circuits of the first workpiece 100.

As shown in FIG. 1C, the exposed portion of the first conductive lines 108 a and 108 b may be partially etched away, thereby forming a first recess 120, as the etch process continues toward the first conductive lines 108 c and 108 d. The exposed portion of the first conductive lines 108 c and 108 d may be partially etched, thereby forming a second recess 122, as the etch process continues toward the first conductive lines 108 e and 108 f. The exposed portion of the first conductive lines 108 e and 108 f may be partially etched, thereby forming a third recess 124, as the etch process continues toward the second conductive line 208 a. Depths of the first recess 120, the second recess 122, and the third recess 124 may vary depending on a variety of applications and design needs.

The selective etch process continues until the second conductive line 208 a is exposed, thereby forming a combined opening extending from a backside of the first workpiece 100 to the second conductive line 208 a of the second workpiece 200 as illustrated in FIG. 1C.

In the illustrated embodiment, the first conductive lines 108 a and 108 b are subject to the etch process longer than the first conductive lines 108 c and 108 d, and the first conductive lines 108 c and 108 d are subject to the etch process longer than the first conductive lines 108 e and 108 f. Therefore, a first depth D₁ of the first recess 120 is larger than a second depth D₂ of the second recess 122, and the second depth D₂ of the second recess 122 is larger than a third depth D₃ of the third recess 124.

It should be noted that the selective etch process may extend through a variety of various layers used to form the one or more first STI regions 109, the first IMD layers 104, the second IMD layers 204, the first passivation layer 106, and the second passivation layer 206, which may include various types of materials and etch stop layers. Accordingly, the selective etch process may utilize multiple etchants to etch through the various layers, wherein the etchants are selected based upon the materials being etched.

In some embodiments, the patterned mask 116 may be fully consumed during the selective etch process described above. In other embodiments, a portion of the patterned mask 116 may still remain on the backside of the first workpiece 100 after the selective etch process is completed. The remaining patterned mask 116 may be removed by using suitable stripping techniques such as chemical solvent cleaning, plasma ashing, dry stripping and/or the like. The techniques are well known and hence are not discussed in further detail herein to avoid repetition.

FIG. 1D illustrates conductive materials formed within the first opening 110 and the second opening 118 in accordance with various embodiments. In some embodiments, the conductive materials may be formed by depositing one or more diffusion and/or barrier layers and depositing a seed layer (not shown). For example, a diffusion barrier layer 126 comprising one or more layers of Ta, TaN, TiN, Ti, CoW, or the like is formed along the sidewalls of the first opening 110 and the second opening 118. The seed layer may be formed of copper, nickel, gold, any combination thereof and/or the like. The diffusion barrier layer and the seed layer may be formed by suitable deposition techniques such as PVD, CVD and/or the like. Once the seed layer has been deposited in the openings, a conductive material, such as tungsten, titanium, aluminum, copper, any combinations thereof and/or the like, is filled into the first opening 110 and the second opening 118, using, for example, an electro-chemical plating process, thereby forming a conductive plug 128 (also referred as a trough oxide via (TOV)).

FIG. 1D also illustrates removal of excess materials, e.g., excess conductive materials, from the backside of the first substrate 102. In some embodiments, the dielectric film 114 may be left along the backside of the first substrate 102 to provide additional protection from the environment. In the example illustrated in FIG. 1D, the dielectric film 114 remains on the backside of the first substrate 102. In this example, the excess materials may be removed using an etch process, a planarization process (e.g., a CMP process), or the like, using the dielectric film 114 as a stop layer.

FIG. 1D further illustrates a dielectric capping layer 130 formed along a backside of the first workpiece 100. In some embodiments, the dielectric capping layer 130 is similar to the first passivation layer 106 described above, is formed using similar materials and methods, and the description is not repeated herein.

In some embodiments, the conductive plug 128 provides electrical connection between some or all of the first conductive lines 108 a-108 f and the second conductive line 208 a, which in turn provides electrical connection between electrical circuits of the first workpiece 100 and the second workpiece 200. For example, the conductive plug 128 may electrically connect the backside of the first substrate 102 to the second conductive line 208 a, the first conductive lines 108 a-108 f to the second conductive line 208 a, or the backside of the first substrate 102 to the first conductive lines 108 a-108 f and the second conductive line 208 a.

As shown in FIG. 1D, the conductive plug 128 comprises five portions. A first portion is from the second conductive line 208 a to the first conductive lines 108 e and 108 f. The first portion is of a first width W₁ as shown in FIG. 1D. A second portion is from the first conductive lines 108 e and 108 f to the first conductive lines 108 c and 108 d. The second portion is of a second width W₂ as shown in FIG. 1D. A third portion is from the first conductive lines 108 c and 108 d to the first conductive lines 108 a and 108 b. The third portion is of a third width W₃ as shown in FIG. 1D. A fourth portion is from the first conductive lines 108 a and 108 b to the front side of the first substrate 102. The fourth portion is of a fourth width W₄ as shown in FIG. 1D. A fifth portion is from the front side of the first substrate 102 to the backside of the first substrate 102. The fifth portion has the fourth width W₄ and a fifth width W₅ as shown in FIG. 1D.

In some embodiments, the fifth width W₅ is greater than the fourth width W₄, the fourth width W₄ is greater than the third width W₃, the third width W₃ is greater than the second width W₂, and the second width W₂ is greater than the first width W₁. The first width W₁ may be between about 0.4 μm and about 2.0 μm. The second width W₂ may be between about 0.6 μm and about 4.0 μm. The third width W₃ may be between about 0.8 μm and about 6.0 μm. The fourth width W₄ may be between about 1.0 μm and about 8.0 μm. The fifth width W₅ may be between about 1.2 μm and about 11 μm.

It should further be noted while FIGS. 1A-1D illustrate conductive lines (e.g., the first conductive lined 108 a-108 f) that function as hard mask layers, one skilled in the art will recognize that other features may also be used as hard mask layers. For example, a plurality of isolation regions, poly-silicon regions, any combinations thereof and/or the like may be used as the hard mask layers.

FIG. 1E illustrates exemplary top views of the first conductive lines 108 a and 108 b in accordance with various embodiments of the present disclosure. While the cross sectional views of the first conductive lines 108 a and 108 b show that the first conductive line 108 a and the first conductive line 108 b are two separate conductive lines (see FIGS. 1A-1D), the first conductive lines 108 a and 108 b may form a continuous annular shaped region as viewed from top as shown in FIG. 1E. In the illustrated embodiment, the inside diameter of the annular shaped region is equal to the third width W₃.

It should be noted that inside and outside surfaces of the annular shaped regions as illustrated in FIG. 1E are for illustrative purpose only and the inside and outside surfaces may have variety of shapes, such as square, circle, oval, triangular, polygonal and/or the like. In some embodiments, the first conductive lines 108 c and 108 d, and the first conductive lines 108 e and 108 f may also form annular shaped regions as viewed from top. The annular shapes of the first conductive lines 108 c and 108 d, and the first conductive lines 108 e and 108 f may be similar to those illustrated in FIG. 1E. However, inside diameters of the annular shaped regions for the first conductive lines 108 c and 108 d, and the first conductive lines 108 e and 108 f are equal to the second width W₂ and the first width W₁, respectively.

FIG. 2 illustrates an interconnect structure between two bonded workpieces in accordance with some embodiments. In what follows, unless otherwise noted, features of FIG. 2 having reference numerals of the form “3xx” and “4xx” are similar to features of FIGS. 1A-1E having reference numerals “1xx” and “2xx,” respectively. For example, an “<element>3xx” of FIG. 2 corresponds to an “<element>1xx” of FIGS. 1A-1E, and an “<element>4xx” of FIG. 2 corresponds to an “<element>2xx” of FIGS. 1A-1E.

Referring further to FIG. 2, a conductive plug 328 interconnecting a first workpiece 300 and a second workpiece 400 is illustrated. In the illustrated embodiment, the first workpiece 300 and the second workpiece 400 and bonded and the conductive plug 328 is formed, for example, using methods as described above with reference to FIGS. 1A-1D and the description is not repeated herein.

As the technology node shrinks, dimensions of various features of semiconductor devices are also reduced. In the embodiment illustrated in FIG. 2, the first conductive lines 308 a-308 f may be so thin that at least some of the first conductive lines 308 a-308 f will be fully etched during the selective etch process. As shown in FIG. 2, the first conductive lines 308 a-308 d may be fully etched away and may fail to reduce a width of the conductive plug 328 as the etch process continues toward the first conductive lines 108 e and 108 f. In the illustrated embodiment, the first conductive lines 108 a-108 d are subject to the selective etch process longer than the first conductive lines 108 e and 108 f. Accordingly, the first conductive lines 108 a-108 d are fully etched away while the first conductive lines 108 e and 108 f are partially etched, thereby forming a recess having a fourth depth D₄. The fourth depth D₄ may vary depending on a variety of applications and design needs.

As shown in FIG. 2, the conductive plug 328 comprises three portions. A first portion is from the second conductive line 408 a to the first conductive lines 308 e and 308 f. The first portion is of a sixth width W₆ as shown in FIG. 2. A second portion is from the first conductive lines 308 e and 308 f to the front side of the first substrate 302. The second portion is of a seventh width W₇ as shown in FIG. 2. A third portion is from the front side of the first substrate 302 to the backside of the first substrate 302. The third portion has the seventh width W₇ and a eighth width W₈ as shown in FIG. 2.

In some embodiments, the eighth width W₈ is greater than the seventh width W₇, and the seventh width W₇ is greater than the sixth width W₆. The sixth width W₆ may be between about 0.4 μm and about 2.0 μm. The seventh width W₇ may be between about 0.6 μm and about 8.0 μm. The eighth width W₈ may be between about 1.2 μm and about 11 μm.

As shown in FIG. 2, the first conductive line 308 a and the first conductive line 308 b are two separate conductive lines. However, in some embodiments, the first conductive lines 308 a and 308 b may form a continuous annular shaped region, similar to one described above with respect to FIG. 1E. In the illustrated embodiment, the inside diameter of the annular shaped region for the first conductive lines 308 a and 308 b is equal to the seventh width W₇. In some embodiments, the first conductive lines 308 c and 308 d, and the first conductive lines 308 e and 308 f may also form annular shaped regions as viewed from top. In the illustrated embodiment, inside diameters of the annular shaped regions for the first conductive lines 308 c and 308 d, and the first conductive lines 308 e and 308 f are equal to the seventh width W₇ and the sixth width W₆, respectively

FIGS. 3A-3H illustrate an interconnect structure between two bonded workpieces in accordance with some embodiments. In what follows, unless otherwise noted, features of FIGS. 3A-3H having reference numerals of the form “5xx” and “6xx” are similar to features of FIGS. 1A-1E having reference numerals “1xx” and “2xx,” respectively. For example, an “<element>5xx” of FIGS. 3A-3H corresponds to an “<element>1xx” of FIGS. 1A-1E, and an “<element>6xx” of FIGS. 3A-3H corresponds to an “<element>2xx” of FIGS. 1A-1E.

Referring first to FIG. 3A, a conductive plug 528 interconnecting a first workpiece 500 and a second workpiece 600 is illustrated. In the illustrated embodiment, the first workpiece 500 and the second workpiece 600 are bonded and the conductive plug 528 is formed, for example, using methods as described above with reference to FIGS. 1A-1D and the description is not repeated herein.

Referring further to FIG. 3A, an embodiment similar to one shown in FIG. 2 is illustrated. In the illustrated embodiment, in addition to first conductive lines 508, first conductive vias 538 a-538 d (collectively referred as first conductive vias 538) are formed within the first IMD layers 504. In some embodiments, the first conductive vias 538 may be formed using, for example, materials and methods described above with respect to the first conductive lines 108 of FIG. 1A, and the description is not repeated herein. In the illustrated embodiment, the first conductive vias 538 electrically interconnect the first conductive lines 508. In some embodiments, the first conductive vias 538 may also function as hard mask layers and may aid in forming a conductive plug 528.

As shown in FIG. 3A, the conductive plug 528 comprises three portions. A first portion is from the second conductive line 608 a to the first conductive lines 508 e and 508 f. The first portion is of the sixth width W₆ as shown in FIG. 3A. A second portion is from the first conductive lines 508 e and 508 f to the front side of the first substrate 502. The second portion is of the seventh width W₇ as shown in FIG. 3A. A third portion is from the front side of the first substrate 502 to the backside of the first substrate 502. The third portion has the seventh width W₇ and the eighth width W₈ as shown in FIG. 3A.

As shown in FIG. 3A, the first conductive line 508 a and the first conductive line 508 b are two separate conductive lines. However, in some embodiments, the first conductive lines 508 a and 508 b may form a continuous annular shaped region, similar to one described above with respect to FIG. 1E. In the illustrated embodiment, the inside diameter of the annular shaped region for the first conductive lines 508 a and 508 b is equal to the seventh width W₇. In some embodiments, the first conductive lines 508 c and 508 d, and the first conductive lines 508 e and 508 f may also form annular shaped regions as viewed from top. In the illustrated embodiment, inside diameters of the annular shaped regions for the first conductive lines 508 c and 508 d, and the first conductive lines 508 e and 508 f are equal to the seventh width W₇ and the sixth width W₆, respectively

In some embodiments, the first conductive vias 538 a and 538 b, and the first conductive vias 538 c and 538 d may also form annular shaped regions as viewed from top. In the illustrated embodiment, inside diameters of the annular shaped regions for the first conductive vias 538 a and 538 b, and the first conductive vias 538 c and 538 d are larger than the seventh width W₇, and, in this embodiment, the first conductive lines 508 a-508 f function as hard mask layers.

In some embodiments, the first conductive lines 508 and first conductive vias 538 collectively form a seal ring structure surrounding the conductive plug 528. In addition to one or more barrier layers 526, the seal ring structure may protect the first IMD layers 504 from diffusion of a conductive material forming the conductive plug 528.

As illustrated in FIG. 3A, portions of the first IMD layers 504 are interposed between the conductive plug 528 and the first conductive vias 538 a-538 d. In some embodiments, the first IMD layers 504 may be laterally etched while forming an opening in the first IMD layers 504 for the conductive plug 528. Furthermore, individual dielectric layers of the first IMD layers 504 may have different etch rates. In some embodiments, dielectric layers of the first IMD layers 504 that are interposed between the first conductive lines 508 a, 508 b and 508 g and the first passivation layer 506 have higher etch rates than dielectric layers of the first IMD layers 504 that are interposed between the first substrate 502 and the first conductive lines 508 a, 508 b and 508 g. An example of such an embodiment is illustrated in FIG. 3B, wherein the first conductive lines 508 a-508 f function as hard mask layers, and portions of the first IMD layers 504 enclosed by annular shaped regions formed of the first conductive vias 538 a-538 b and the first conductive vias 538 c-538 d are fully etched by a lateral etch process, while portions of the first IMD layers 504 interposed between the first conductive lines 508 a-508 b and the first substrate 502 are not substantially etched by the lateral etch process. In the illustrated embodiment, the conductive plug 528 is in direct electrical contact with the first conductive vias 538 a-538 d. In alternative embodiments, the lateral etch process may not fully remove the portions of the first IMD layers 504 enclosed by the annular shaped regions formed of the first conductive vias 538 a-538 b and the first conductive vias 538 c-538 d depending on inside diameters of the annular shaped regions. In such embodiments, portions of the first IMD layers 504 remain interposed between the conductive plug 528 and the first conductive vias 538 a-538 d.

Referring to FIG. 3C, an embodiment similar to one shown in FIG. 3A is illustrated. In the illustrated embodiment, inside diameters of annular shaped regions for the first conductive lines 508 a and 508 b, the first conductive lines 508 c and 508 d, and the first conductive lines 508 e and 508 f are equal to the seventh width W₇, the seventh width W₇, and the sixth width W₆, respectively. In addition, inside diameters of annular shaped regions for the first conductive vias 538 a and 538 b, and the first conductive vias 538 c and 538 d are equal to the seventh width W₇, and, in this embodiment, the first conductive lines 508 a-508 f and the first conductive vias 538 a-538 d function as hard mask layers.

Referring to FIG. 3D, an embodiment is illustrated, wherein the first conductive lines 508 a-508 f and the first conductive vias 538 b and 538 d function as hard mask layers. In the illustrated embodiment, portions of the first IMD layers 504 adjacent to the first conductive vias 538 a and 538 c are fully etched by a lateral etch process, and the conductive plug 528 is in direct electrical contact with the first conductive vias 538 a and 538 c. As shown in FIG. 3D, inside diameters of annular shaped regions for the first conductive lines 508 a and 508 b, and the first conductive lines 508 c and 508 d, are equal to the seventh width W₇, and an inside diameter of an annular shaped region for the first conductive lines 508 e and 508 f is equal to the sixth width W₆.

Referring to FIG. 3E, an embodiment is illustrated, wherein inside diameters of annular shaped regions for the first conductive lines 508 a and 508 b, and the first conductive lines 508 c and 508 d, are larger than the seventh width W₇, and an inside diameter of an annular shaped region for the first conductive lines 508 e and 508 f is equal to the sixth width W₆. In addition, inside diameters of annular shaped regions for the first conductive vias 538 a and 538 b, and the first conductive vias 538 c and 538 d are equal to the seventh width W₇, and, in this embodiment, the first conductive lines 508 e-508 f and the first conductive vias 538 a-538 d function as hard mask layers.

Referring to FIG. 3F, an embodiment is illustrated, wherein the conductive plug 528 comprises four portions. A first portion is from the second conductive line 608 a to the first conductive lines 508 e and 508 f. The first portion is of the sixth width W₆ as shown in FIG. 3F. A second portion is from the first conductive lines 508 e and 508 f to the first conductive lines 508 c and 508 d. The second portion is of a ninth width W₉ as shown in FIG. 3F. In some embodiments, the ninth width W₉ is between about 0.6 μm and about 4.0 μm. A third portion is from the first conductive lines 508 c and 508 d to the front side of the first substrate 502. The third portion is of the seventh width W₇ as shown in FIG. 3F. A fourth portion is from the front side of the first substrate 502 to the backside of the first substrate 502. The fourth portion has the seventh width W₇ and the eighth width W₈ as shown in FIG. 3F. In the illustrated embodiment, the first conductive lines 508 a-508 f and the first conductive vias 538 a and 538 b function as hard mask layers, and the first conductive lines 508 c-508 f are partially etched.

Referring to FIG. 3G, an embodiment is illustrated, wherein the conductive plug 528 has an asymmetric shape and comprises four portions. A first portion is from the second conductive line 608 a to the first conductive lines 508 e and 508 f. The first portion is of the sixth width W₆ as shown in FIG. 3G. A second portion is from the first conductive lines 508 e and 508 f to the first conductive lines 508 c and 508 d. The second portion is of a tenth width W₁₀ as shown in FIG. 3G. In some embodiments, the tenth width W₁₀ is between about 0.6 μm and about 4.0 μm. A third portion is from the first conductive lines 508 c and 508 d to the front side of the first substrate 502. The third portion is of the seventh width W₇ as shown in FIG. 3G. A fourth portion is from the front side of the first substrate 502 to the backside of the first substrate 502. The fourth portion has the seventh width W₇ and the eighth width W₈ as shown in FIG. 3G. In the illustrated embodiment, the first conductive lines 508 a-508 f and the first conductive vias 538 b and 538 d function as hard mask layers, and the first conductive lines 508 d-508 f are partially etched.

Referring to FIG. 3H, an embodiment is illustrated, wherein inside diameters of annular shaped regions for the first conductive lines 508 a and 508 b, and the first conductive lines 508 c and 508 d are larger than the seventh width W₇, and an inside diameter of an annular shaped region for the first conductive lines 508 e and 508 f is equal to the sixth width W₆. In addition, inside diameters of the annular shaped regions for the first conductive vias 538 a and 538 b, the first conductive vias 538 c and 538 d, and first conductive vias 538 e and 538 f are larger than the seventh width W₇, and, in this embodiment, the first conductive lines 508 e and 508 f function as a hard mask layer.

In some embodiments, further process steps may be performed on stacked workpieces illustrated in FIGS. 1D, 2, and 3A-3H. For example, FIG. 3I illustrates further process steps that are performed on stacked workpieces illustrated in FIG. 3H. In some embodiments, a bond pad 701 is formed in the dielectric capping layer 530 and contacts the conductive plug 528. The bond pad 701 may be formed of a conductive material such as aluminum, although other suitable materials, such as copper, tungsten, or the like, may alternatively be utilized. In some embodiment, the dielectric capping layer 530 may be patterned using, for example, a photolithographic masking and etching process to form openings in the dielectric capping layer 530 to expose the conductive plug 528. The material of the bond pad 701 may be deposited to fill the openings using a process such as CVD, PVD, plating, or the like. Once the material of the bond pad 701 has been deposited, any excessive material overfilling the openings may be removed using an etch process, a planarization process (e.g., a CMP process), or the like, such that the topmost surface of the bond pad 701 is substantially coplanar with the topmost surface of the dielectric capping layer 530.

In some embodiments, a connector 703 such as a wire bond is utilized to allow for electrical connection to components and systems external to the stacked workpieces illustrated in FIG. 3I. In an embodiment, an electronic flame off (EFO) wand may be used to raise the temperature of a gold wire within a capillary controlled by a wire clamp (not illustrated). Once the temperature of the gold wire is raised to between about 150° C. and about 250° C., the gold wire is contacted to the bond pad 701 to form the wire bond. Another end of the wire of the wire bond is then contacted and bonded to a bonding pad of an external system to provide electrical connection. One skilled in the art will recognize that connectors such as ball bonds, solder bumps, micro bumps, copper pillars, and the like may also be used to electrically connect the stacked workpieces of FIG. 3I to external devices. Moreover, one skilled in the art will recognize that a plurality of bond pads and corresponding connectors (such as the bond pad 701 and the corresponding connector 703) may be utilized to provide electrical connections to external devices.

The method of forming the bond pad 701 and the connector 703 as described above with reference to FIG. 3I is provided for illustrative purposes only. In other embodiment, formation of bond pads and corresponding connectors may further include, for example, formation of one or more passivation layers, formation of one or more redistribution layers (RDLs), formation of one or more under bump metallurgies (UBMs), or the like over the stacked workpieces of FIG. 3I.

FIG. 4 is a flowchart illustrating a method of forming an interconnect in stacked workpieces in accordance with some embodiments. The method begins in step 702, wherein substrates to be bonded are provided. The workpieces may be processed wafers (such as those illustrated in FIG. 1A), dies, a wafer and a die, or the like.

In step 704, the workpieces are bonded and a first opening is formed in a first substrate of a first workpiece. A patterned mask is formed on the first substrate, the patterned mask defining an opening for a contact plug to be subsequently formed, such as that discussed above with reference to FIG. 1B. Optionally, an ARC layer and/or one or more hard mask layers are formed. Thereafter, a first etch process is performed to etch through the first substrate, such as discussed above with reference to FIG. 1B, thereby forming the first opening.

In step 706, one or more dielectric films are formed within the first opening and along a backside of the first substrate as discussed above with reference to FIG. 1B. A patterned mask, as discussed above with reference to FIG. 1B, is formed to define a second opening to contact select ones of the interconnects formed on the first substrate and/or a second substrate of a second workpiece in step 708. In step 710, another etch process is used to create the second opening while using some of the interconnects formed on the first substrate as hard mask layers, which exposes portions of the interconnects on the first substrate and/or the second substrate, as discussed above with reference to FIG. 1C. The first opening and the second opening are filled with a conductive material in step 712, such as that discussed above with reference to FIG. 1D. A dielectric cap layer may be formed over the conductive material, such as that discussed above with reference to FIG. 1D.

One advantageous feature of the above described method is that the method allows reduction of a conductive plug critical dimension below a dimension achievable, for example, by conventional photolithography methods. Accordingly, by interconnecting bonded workpieces using conductive plugs as described above with respect to FIGS. 1A-3H semiconductor devices with reduced form factors may be formed. In addition, forming a seal ring around the conductive plug as illustrated in FIGS. 3A-3H may provide addition protection to layers surrounding the conductive plug.

According to an embodiment, a semiconductor device comprises a first substrate having a first side and a second side opposite the first side, and first vertically stacked interconnects formed within respective first dielectric layers on the first side of the first substrate. The semiconductor device further comprises a second substrate having a third side and a fourth side opposite the third side, the first side of the first substrate facing the third side of the second substrate, second interconnects formed within respective second dielectric layers on the third side of the second substrate, and a conductive plug extending from the second side of the first substrate to a first conductive feature of the second interconnects, the conductive plug extending through at least two conductive features of the first vertically stacked interconnects.

According to another embodiment, a semiconductor device comprises a first workpiece having a first side and a second side opposite the first side, the first workpiece comprising first dielectric layers formed on the first side, the first dielectric layers having a first interconnect and a second interconnect formed therein, wherein the first interconnect and the second interconnect have an annular ring shape, and a second workpiece bonded to the first workpiece, the second workpiece comprising second dielectric layers formed on a third side of the second workpiece, the second dielectric layers having a third interconnect formed therein, wherein the first side of the first workpiece faces the third side of the second workpiece. The semiconductor device further comprises a conductive plug extending from the second side of the first workpiece to the third interconnect. The conductive plug comprises a first portion extending from the third interconnect to the second interconnect, and a second portion extending from the second interconnect to the first interconnect, wherein a width of the second portion is larger than a width of the first portion.

According to yet another embodiment, a method of forming a semiconductor device, the method comprises providing a first workpiece having a first side and a second side opposite the first side, the first workpiece having first vertically stacked interconnects formed in first dielectric layers on the first side, providing a second workpiece, the second workpiece having a second interconnect formed in second dielectric layers on a third side of the second workpiece, and bonding the first workpiece to the second workpiece such that the first side of the first workpiece faces the third side of the second workpiece. The method further comprises forming an opening on the second side the first workpiece, the opening extending through at least two interconnects of the first vertically stacked interconnects, the opening exposing at least a portion the second interconnect, and filling the opening with a conductive material.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A semiconductor device comprising: a first substrate having a first side and a second side opposite the first side; a shallow trench isolation (STI) region in the first substrate; first vertically stacked interconnects within respective first dielectric layers on the first side of the first substrate; a second substrate having a third side and a fourth side opposite the third side, the first side of the first substrate facing the third side of the second substrate; second interconnects within respective second dielectric layers on the third side of the second substrate; and a conductive plug extending from the second side of the first substrate to a first conductive feature of the second interconnects, the conductive plug extending through the STI region and at least two conductive features of the first vertically stacked interconnects, wherein a width of the conductive plug narrows as the conductive plug extends from a first side of the STI region to a second side of the STI region, and wherein the second side of the STI region is a closest side of the STI region from the first vertically stacked interconnects.
 2. The semiconductor device of claim 1, wherein the first vertically stacked interconnects form a seal ring surrounding the conductive plug.
 3. The semiconductor device of claim 2, wherein a portion of the first dielectric layers is interposed between the conductive plug and the seal ring.
 4. The semiconductor device of claim 1, wherein the first vertically stacked interconnects comprise conductive lines.
 5. The semiconductor device of claim 4, wherein the first vertically stacked interconnects further comprise conductive vias.
 6. The semiconductor device of claim 1, wherein the first vertically stacked interconnects have annular shapes.
 7. The semiconductor device of claim 1, wherein the conductive plug comprises a first portion extending from the first conductive feature of the second interconnects to the first vertically stacked interconnects, and a second portion extending through the at least two conductive features of the first vertically stacked interconnects, a width of the second portion being larger than a width of the first portion.
 8. The semiconductor device of claim 7, wherein the conductive plug further comprises a third portion extending through the first substrate, a width of the third portion being larger than the width of the second portion.
 9. A semiconductor device comprising: a first workpiece having a first side and a second side opposite the first side, the first workpiece comprising first dielectric layers on the first side, the first dielectric layers having a first interconnect and a second interconnect therein, wherein the first interconnect and the second interconnect have an annular ring shape; a second workpiece bonded to the first workpiece, the second workpiece comprising second dielectric layers on a third side of the second workpiece, the second dielectric layers having a third interconnect therein, wherein the first side of the first workpiece faces the third side of the second workpiece; and a conductive plug extending from the second side of the first workpiece to the third interconnect, the conductive plug comprising: a first portion extending from the third interconnect to the second interconnect; a second portion extending from the second interconnect to the first interconnect, wherein a width of the second portion is larger than a width of the first portion; and a third portion, the third portion extending through a first substrate of the first workpiece, a width of the third portion being larger than the width of the second portion.
 10. The semiconductor device of claim 9, wherein the first interconnect and the second interconnect are part of a seal ring, the seal ring surrounding the second portion of the conductive plug.
 11. The semiconductor device of claim 10, wherein a portion of the first dielectric layers interposed between the seal ring and the conductive plug is free from conductive features.
 12. The semiconductor device of claim 10, wherein the seal ring is electrically coupled to the conductive plug.
 13. The semiconductor device of claim 10, wherein the conductive plug extends through a shallow trench isolation (STI) region in the first workpiece.
 14. A semiconductor device comprising: a first substrate; one or more first metallization layers on a first side of the first substrate, the one or more first metallization layers comprising a stack of first interconnects; a first insulating layer on the first side of the first substrate, the one or more first metallization layers being interposed between the first substrate and the first insulating layer; a second substrate; one or more second metallization layers on a first side of the second substrate; a second insulating layer on the first side of the second substrate, the one or more second metallization layers being interposed between the second substrate and the second insulating layer, the second insulating layer contacting the first insulating layer; a conductive plug extending through the first substrate, the one or more first metallization layers, the first insulating layer and the second insulating layer, and extending into the one or more second metallization layers, the stack of first interconnects surrounding the conductive plug, at least two conductive features of the stack of first interconnects being in direct electrical contact with the conductive plug; and a shallow trench isolation (STI) region on the first side of the first substrate, the conductive plug extending through the STI region, a width of the conductive plug narrowing as the conductive plug extends from an uppermost surface of the STI region to a bottommost surface of the STI region, the uppermost surface of the STI region being a farthest surface of the STI region from the one or more first metallization layers.
 15. The semiconductor device of claim 14, wherein the conductive plug electrically couples the stack of first interconnects and a second interconnect in the one or more second metallization layers.
 16. The semiconductor device of claim 14, wherein the stack of first interconnects forms a seal ring.
 17. The semiconductor device of claim 16, wherein the seal ring comprises conductive lines.
 18. The semiconductor device of claim 17, wherein the seal ring further comprises conductive vias.
 19. The semiconductor device of claim 17, wherein the seal ring separates the conductive plug from other conductive features in the one or more first metallization layers.
 20. The semiconductor device of claim 9, wherein a sidewall of the conductive plug is in physical contact with the second interconnect, and wherein the sidewall of the conductive plug is separated from the first interconnect by at least a portion of the first dielectric layers.
 21. The semiconductor device of claim 9, wherein the conductive plug further comprises a fourth portion extending through the second interconnect, a width of the fourth portion changing as the fourth portion extends through the second interconnect. 